onsemi has marked the CNY173SD as Obsolete. This part is sourced through independent distribution channels — quantities are lot-specific and confirmed at RFQ. No stock-holding claim; availability confirmed per request.
5300Vrms isolation and CTR range
The current transfer ratio (CTR) is specified at 100% minimum and 200% maximum, both at 10mA forward current. That 2:1 spread means the designer must budget enough drive current on the input side and enough pull-up margin on the output side to guarantee the logic threshold is crossed across all temperature and aging conditions.
DC input, transistor output with base access
This is a DC-input optocoupler with a phototransistor output that brings the base terminal out to a separate pin. The base-access pin lets you add a base-emitter resistor to tailor the switching threshold or speed, or to bias the transistor for analog signal transfer. The output transistor is rated for 70V maximum collector-emitter voltage and 50mA continuous current per channel. Vce saturation is 300mV max — at 50mA that's 15mW dissipation in the output stage, well within the package limits at 100°C ambient.
Switching speed and temperature range
Typical turn-on time is 2µs, turn-off time 3µs, with rise and fall times of 1µs and 2µs respectively. These numbers place the CNY173SD in the medium-speed class — adequate for 50/60Hz line synchronisation, relay drivers, and PLC input modules, but not for high-speed digital isolation above a few hundred kHz.